Effects of long-term exposure of tuffs to high-level nuclear waste-repository conditions. Preliminary report Page: 3 of 27
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Several factors can affect the thermomechanical behavior of rocks. Among
these are temperature, stress field, and time. The mechanisms involved are
complex and beyond the scope of this report, but we note that both physical
and chemical processes can result in temporary or permanent changes in the
rocks. Although laboratory measurements are commonly made under a variety of
temperature and stress conditions, the effect of time is seldom measured
because the relatively long time scales required for such tests immobilize
equipment that could otherwise be used for many shorter tests.
This project was designed to test a large number of samples at one time
by an extended exposure to the hot, wet, high-stress conditions expected near
a waste repository. The individual tests are designed to cover a range of tem-
perature and pressure conditions simulating varying distances from the waste
canister and different repository depths. Because the properties of tuffs
vary substantially with lithology, a range of "types" covering varying degrees
of welding and postdeposition mineralization were chosen.
The experiments reported here avoid the need for tying up high-tempera-
ture, high-pressure testing equipment by performing most measurements at
ambient conditions. The samples were exposed to repository conditions in a
sealed environment and later removed for testing. This allows a wide range of
tests on a significant number of samples. By comparing the results of these
tests with similar data for control samples, changes caused by the exposure
can be detected.
These experiments are intended to be exploratory in nature. They were
designed to detect irreversible changes in the physical and mineralogic
character of the samples that may indicate potentially troublesome temperature
or pressure conditions. Any adverse effects noted should be investigated
further by appropriately designed experiments. Because for the most part data
collection is at ambient conditions, the data presented here should not be
regarded as engineering data.
II. SAMPLES AND SAMPLE PREPARATION
Samples for this study were selected from cores taken from two test holes
at the Yucca Mountain Site at the Nevada Test Site. These holes are UE25a#1
and USW-GI. General petrology and mineralogy of the rock units found in these
cores have been reported elsewhere. 1,2 Four units were selected for the tests
shown in Table I. These selections were made to provide a contrast in degree
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Blacic, J.; Carter, J.; Halleck, P.; Johnson, P.; Shankland, T.; Andersen, R. et al. Effects of long-term exposure of tuffs to high-level nuclear waste-repository conditions. Preliminary report, report, February 1, 1982; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc696551/m1/3/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.